Surface observations and material removal mechanisms in rotary ultrasonic machining of brittle material

The numerous unique advantages afforded by rotary ultrasonic machining have led to its extensive utilization in machining hard-brittle materials. However, the material removal mechanisms are still not very clear, leaving many uncertainties of the machined components in practical application. In this research, machining/scratching tests had been undertaken on optical glass K9 with diamond tools under various process parameters. Surface morphologies were characterized using a measuring microscope, white-light interferometer and scanning electron microscope. On the basis of these examinations, the effects of ultrasonic vibration on the material removal mechanisms were investigated. As a result, another material removal mechanism, pulverization, was identified besides brittle fracture and plastic deformation. The pulverizable areas, which resulted from the force of the tortuous cracks propagation, were found to be prominent in the surrounding fracture areas. In addition, the influence of the pulverizable areas on the surface roughness was also investigated. The scratching results presented that the pulverization was induced by the impact effects of the abrasive at the vertex of its sinusoidal trajectory. The vertical inertia force of the abrasive and the inertial effects of the material, which were induced by the immense acceleration of single abrasive at the vertex of its sinusoidal trajectory, should be conducive to the nucleation of the first cracks.